The present invention relates to an addressing method in a digital telecommunications network, as well as to a name and address server implementing such a method.
The invention belongs to the field of the addressing of networked machines. It applies more particularly to a digital telecommunications network having first and second addressing zones, between which an interface unit caters for address translations.
Specifically, if the addressing used in the first zone is different from that used in the second zone, the communication between a source machine situated in one zone and a destination machine situated in the other zone requires in particular the translation of the addresses assigned to these machines, at the level of the interface between the two addressing zones.
IP (“Internet Protocol”) addressing, that is to say the address allocation mode used by Internet, is generally an addressing of dynamic type in low-speed on-line networks.
When a customer connects to an Internet service provider, or ISP, which communicates with this customer by means of a private address, the ISP allots an address from a list of public IP addresses which it holds. The customer can then communicate with the public domain by means of the public address which has been allotted to him. As soon as the customer disconnects, the address which had been allotted to him becomes available again for another user.
This organization has hitherto been rendered possible by the fact that the customers of ISPs are often wont to disconnect, on the one hand because the charge is often dependent on the duration of the connections, and on the other hand because these customers wish to free their telephone line so as to be able to be contacted.
However, there is currently a trend to bill at a flat rate rather than as a function of the duration of the connections, so that the number of disconnections will likely tend to diminish.
Furthermore, the customers are no longer necessarily constrained to disconnect in order to free their telephone line, given that there are relatively recent telecommunications techniques allowing the simultaneous use of the telephone service and consultation services. Among these techniques may be cited for example the use of a separate medium such as cable, or else the implementation of ADSL (“Asymmetric Digital Subscriber Line”) links.
Within such a context of economic and technical change, customers are no longer likely to suffer the constraint of having to disconnect as often as hitherto. In this case, the use of the aforesaid technique will no longer be suitable for recovering the IP address of a customer with a view to reallocating it.
As a solution for remedying the lack of public addresses, under certain conditions it is possible to use a private addressing, that is to say to allocate the customer a private address and then on exiting the private zone controlled by the ISP to carry out an address translation with the aid of the NAT function.
The NAT or network address translation function, generally installed at a point of exit of the private domain which uses specific local addressing, implements the aforesaid dynamic addressing: it manages a list of public IP addresses and matches a private address of a calling machine with an IP address picked from the list, and performs an address translation in respect of each packet arriving at the NAT point and which travels from the calling machine of the private domain to a contacted machine of the public domain.
Thus, for the contacted machine, everything happens as if the address of the calling machine of the private domain were the public address contained in the list of IP addresses.
The contacted machine therefore responds to the calling machine to this address, and when a response packet arrives at the NAT point, the router effects the translation of the address contained in the list of IP addresses to the destination private address and forwards the packet in the private domain to the calling machine.
A drawback of this addressing mechanism is that it does not allow a machine of the public addressing domain to send a packet to a machine of the private addressing domain without action by the latter machine, since the matching of the addresses is dynamic, hence temporary, and since the private address is unknown to the routing tables.
Furthermore, within the framework of new applications such as Internet telephony, it is currently necessary to possess an IP address in order to be able to be contacted, so that the data packets can be routed to the corresponding machine.